EP4107534B1 - Apparatus and method for locating partial discharges in medium-voltage and high-voltage equipment - Google Patents

Description

The present invention relates to devices and methods for locating partial discharges in medium or high voltage equipment. In particular, the present invention relates to such devices and methods that can be used to locate partial discharges in medium or high voltage equipment with complex winding structures.

BACKGROUND OF THE INVENTION

Medium or high voltage equipment can fail due to a short circuit if its conductor insulation is damaged. The first signs of this damage are often revealed by partial discharge measurements. In addition to determining whether partial discharges (PD) are active, it is crucial to localize the location where the PD originates.

Depending on the equipment, there are different methods to locate a PD.

Electromagnetic methods, for example, scan a winding using a sensor, such as a coil with a ferrite core, and record a PD-related voltage swing in the mV range. It is also possible to subject PD-related electrical impulses to a signal propagation time analysis in power cables. Other electromagnetic methods analyze PD-related radio waves.

Acoustic methods scan a winding, and in particular a winding head, using sound measurements. Surface-near phenomena are easier to detect than defects in the winding. For example, acoustic signals can be triangulated in oil-filled equipment.

Optical methods subject a winding to a light measurement, since TE emits not only noise but also light, which can be separated from daylight using appropriate filters. In this case, only surface phenomena are detected.

However, these methods cannot be used for rotating electrical machines: Due to the complex winding structure, parallel propagation paths for electrical impulses arise, which means that a signal propagation time analysis cannot be carried out. Acoustic location cannot be used either due to the solid insulation and the lack of accessibility of the winding.

The known methods have in common that there is no assignment of the partial discharge to the electrically measured pulse at the connections and therefore no assignment to the apparent charge (cf. phase-resolved partial discharge, PRPD). The latter would be necessary for a reliable statement as to how energetic the partial discharge can be at its origin. Furthermore, the effort in terms of sensors and measurement increases, since a series of measurements must be carried out in order to be able to determine the origin of the partial discharge. Furthermore, the winding may have to be made accessible, which significantly increases the measurement effort again.

A device for locating a partial discharge in a medium or high voltage equipment according to the preamble of claim 1 and a corresponding method according to the preamble of claim 10 are known from the document EP 2 360 486 A1 known.

Furthermore, the publication " A Review of Online Partial Discharge Measurement of Large Generators", Luo Yuanlin et al, ENERGIES, Vol. 10, No. 11, October 25, 2017, page 1694, XP055804886 In the context of localizing partial discharges for a winding system such as a generator or motor, it is known that there are two different propagation modes for partial discharges, namely a slow, lower frequency, wired propagation mode along the intended conduction path and a fast, higher frequency propagation mode outside the intended conduction path.

SUMMARY OF THE INVENTION

There is a need for improved devices and methods for locating partial discharges in medium or high voltage equipment, especially in equipment with complex winding arrangements (e.g. electrical rotating machines).

This object is achieved by the features of the independent patent claims. The features of the dependent patent claims define preferred or advantageous embodiments.

A first aspect of the invention relates to a device for locating partial discharges in medium or high voltage equipment. The device comprises a signal detection device for detecting an electrical signal quantity of the equipment; a filter device for low-pass filtering the detected electrical signal quantity as a function of a filter cut-off frequency; a time detection device for detecting a signal propagation time of the low-pass filtered electrical signal quantity; and a comparison device for comparing the signal propagation time detected as a function of the filter cut-off frequency with a reference propagation time for charge pulses conducted through the equipment. Finally, the location of the respective partial discharge in the equipment can be determined on the basis of this comparison.

The filter device is arranged to gradually reduce the filter cutoff frequency starting from an initial filter cutoff frequency until a signal propagation time detected at the reduced filter cutoff frequency exceeds a predetermined absolute signal propagation time threshold or exceeds a signal propagation time duration detected at the initial filter cutoff frequency by a predetermined relative signal propagation time ratio.

A step size when reducing the filter cutoff frequency can be at least 0.1 kHz, preferably 1 kHz and more preferably 10 kHz.

The predetermined relative signal propagation time ratio can be at least 2, preferably 5 and particularly preferably 10.

The filter cutoff frequency may be at most 1 MHz, preferably at most 100 kHz, and particularly preferably at most 50 kHz.

The device may further comprise a charge calibrator for conducting a charge pulse through the operating means in a conductive manner in order to determine the reference propagation time for this charge pulse.

The invention can preferably be implemented digitally. The detected electrical signal quantity can therefore comprise digital voltage values, and the signal detection device can comprise a voltmeter providing digital voltage values. The filter device can comprise a digital low-pass filter. The time detection device can comprise a timer providing digital time values. The comparison device can comprise an arithmetic or calculation unit providing a comparison result of the detected signal propagation time with the reference propagation time.

A second aspect of the invention relates to a method for locating partial discharges in medium or high voltage equipment. The method comprises detecting an electrical signal quantity of the equipment; low-pass filtering the detected electrical signal quantity as a function of a filter cut-off frequency; detecting a signal propagation time of the low-pass filtered electrical signal quantity; and comparing the signal propagation time detected as a function of the filter cut-off frequency with a reference propagation time for charge pulses conducted through the entire equipment in a conductive manner.

The method further comprises gradually reducing the filter cutoff frequency starting from an initial filter cutoff frequency until a signal propagation time detected at the reduced filter cutoff frequency exceeds a predetermined absolute signal propagation time threshold or exceeds a signal propagation time duration detected at the initial filter cutoff frequency by a predetermined relative signal propagation time ratio.

The method may further comprise conducting a charge pulse through equipment or along equipment to determine the reference propagation time prior to localizing the partial discharge.

The method may also include determining a frequency range of the electrical signal quantity in which a low-frequency component of the partial discharge dominates over a high-frequency component of the partial discharge. In the detected frequency range, the signal propagation time of the electrical signal quantity is determined and compared with the reference propagation time in order to determine the location of the partial discharge in the equipment depending on the comparison result.

In general, the method according to the invention can be carried out in an automated or computer-aided manner using the device according to the invention according to one of the embodiments described herein.

SHORT DESCRIPTION OF THE CHARACTERS

• Fig. 1 veranschaulicht eine Vorrichtung zum Lokalisieren von Teilentladungen in Mittel- oder Hochspannungsbetriebsmitteln nach einem Ausführungsbeispiel.
• Fig. 2 veranschaulicht eine Abhängigkeit eines Amplitudenganges einer Filtereinrichtung zum Tiefpassfiltern einer erfassten elektrischen Signalgröße von einer Filtergrenzfrequenz.
• Fig. 3 veranschaulicht eine Abhängigkeit einer Signalausbreitungszeit einer Teilentladung in dem Betriebsmittel von der Filtergrenzfrequenz.
• Fig. 4 veranschaulicht ein Verfahren zum Lokalisieren von Teilentladungen in Mittel- oder Hochspannungsbetriebsmitteln nach einem Ausführungsbeispiel.

The invention is briefly explained below using preferred embodiments and with reference to the drawings, wherein like reference numerals designate like or similar elements.

• Fig. 1 illustrates a device for locating partial discharges in medium or high voltage equipment according to an embodiment.
• Fig. 2 illustrates a dependence of an amplitude response of a filter device for low-pass filtering a detected electrical signal quantity on a filter cutoff frequency.
• Fig. 3 illustrates a dependence of a signal propagation time of a partial discharge in the equipment on the filter cutoff frequency.
• Fig. 4 illustrates a method for locating partial discharges in medium or high voltage equipment according to one embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention is explained in more detail below using preferred embodiments and with reference to the drawings.

A description of embodiments in specific fields of application does not imply a restriction to these fields of application.

Elements of schematic representations are not necessarily reproduced to scale, but rather in such a way that their function and purpose can be understood by persons skilled in the art.

Unless expressly stated otherwise, the features of the various embodiments can be combined with one another.

Fig. 1 illustrates a device 10 for locating partial discharges in medium or high voltage equipment 20 according to an embodiment.

A medium or high voltage equipment within the meaning of this application can be understood as equipment that can be used at the voltage levels of the high voltage network or the medium voltage network. These can in particular have complex winding structures. Examples of these include electrical rotating machines, power transformers and voltage converters. The invention can also be used for machines in industrial applications.

A partial discharge or pre-discharge within the meaning of this application can be understood as locally occurring, incomplete electrical breakdowns of the insulation of conductor structures in medium- or high-voltage equipment, especially when subjected to alternating voltages.

The in Fig. 1 The device 10 shown on the left comprises a signal detection device 101 for detecting 301 an electrical signal quantity of the Fig. 1 on the right side of the equipment 20. How Fig. 1 illustrated are the outputs from the equipment 20 and in Fig. 1 The terminals of the equipment 20, designated "P(hase)" and "N(eu-tral)", can be electrically connected to the signal detection device 101.

An electrical signal quantity within the meaning of this application can be understood as an electrical current or in particular an electrical voltage (potential difference).

The signal detection device 101 may comprise a voltmeter providing digital voltage values, and the detected electrical signal quantity may accordingly comprise digital voltage values.

This considerably simplifies circuitry and subsequent signal processing.

The device 10 further comprises a filter device 102 for low-pass filtering 302 the detected electrical signal quantity as a function of a filter cutoff frequency fc.

absinkt.A filter cutoff frequency, bend frequency or corner frequency within the meaning of this application can be understood as those frequencies at which an amplitude response of a filtered electrical signal quantity is reduced to a value of $1/\surd 2\approx \mathrm{70,7}\%$

sinks.

An amplitude response within the meaning of this application can be understood as a frequency-dependent relationship between the amplitudes of an input variable and an output variable of a linear time-invariant system, in particular a filter, in the case of sinusoidal excitation.

A signal propagation of PD-related electromagnetic signals/pulses occurs depending on their frequency. The signals can be transmitted through the insulation (high frequency) or via a cable through the copper tracks (low frequency). High-frequency components are therefore radiated, are not connected to a cable and arrive at the signal detection device 101 via the shortest path. Low-frequency components, on the other hand, are connected to a cable and follow the winding geometry.

Fig. 2 illustrates a dependence of an amplitude response of a filter device 102 for low-pass filtering 302 of a detected electrical signal variable on a filter cutoff frequency fc.

, der die jeweilige Filtergrenzfrequenz fc kennzeichnet, und in einem Sperrbereich darunter.The low-pass filter 302 removes the high-frequency components, such as Fig. 2 illustrated by way of example. The amplitude response of the same filter device 102 is shown at ten different filter cut-off frequencies fc from 0.1 MHz to 1 MHz. In a respective passband, the amplitude response of the filtered electrical signal quantity is above the value of $1/\surd 2\approx \mathrm{70,7}\%$

, which indicates the respective filter cutoff frequency fc, and in a stop band below it.

A step-by-step reduction 303 of the filter cutoff frequency fc therefore results in the passband being successively reduced at lower frequencies and the stopband being successively increased at higher frequencies.

Fig. 3 illustrates a dependence of a signal propagation time t(fc) on the filter cutoff frequency fc. The exemplary signal propagation time t(fc) of a TE-related electromagnetic pulse to the signal detection device 101 is shown as a function of a filter cutoff frequency fc that is successively reduced from 1 MHz to approximately 0.1 MHz.

Depending on the filter cutoff frequency fc, the high-frequency component of the signal may initially dominate, such as Fig. 3 This is illustrated by way of example. This spreads out by radiation and arrives at the signal detection device 101 via the shortest path.

The filter device 102 can be configured to gradually reduce 303 the filter cutoff frequency f _c starting from an initial filter cutoff frequency f _C,0 until a signal propagation time t detected at the reduced filter cutoff frequency f _c exceeds a predetermined absolute signal propagation time threshold value trn or exceeds a signal propagation time duration t ₀ detected at the initial filter cutoff frequency f _C,0 by a predetermined relative signal propagation time ratio N.

When the filter cutoff frequency fc is gradually reduced 303, a sudden increase in the signal propagation time t is observed at around 0.35 MHz. This jump is considered a transition in which the low-frequency, conducted component of the detected electrical signal quantity dominates and varies depending on the test object and has been observed in particular in the range < 1 MHz. The gradual reduction 303 can also be extended into the lower MHz range (eg < 10 kHz). The most meaningful results are achieved at filter frequencies of < 100 kHz, even better 10 - 50 kHz.

If the filter cutoff frequency f _C of a test object, where a low-frequency, line-based signal propagation dominates, is known, this can be set or configured directly without requiring a step-by-step reduction 303 of the filter cutoff frequency f _C in the field. With the step-by-step reduction 303 of the filter cutoff frequency f _C , data storage for test object-specific filter cutoff frequencies f _C is therefore unnecessary and the test process is automated.

The low-pass filter 302 eliminates the multipath propagation of the signals through the insulation, which then allows a runtime analysis to be carried out, as is known from power cables. If the winding geometry and the total runtime through the winding are known, a conclusion can be drawn about the location of the PD.

The filter device 102 can in particular comprise a digital low-pass filter.

This considerably simplifies the circuitry effort and the subsequent signal processing, especially with regard to the adjustability of the filter cutoff frequency fc.

The device 10 further comprises a time detection device 104 for detecting 304 a signal propagation time t of the low-pass filtered electrical signal quantity. The time recording device 103 may comprise a timer providing digital time values.

This considerably simplifies the circuit complexity and the subsequent signal processing, in particular with regard to the possibly required storage and processing of a number of signal propagation times for a corresponding number of different filter cutoff frequencies f _C .

The device 10 further comprises a comparison device 105 for comparing 305 the signal propagation time t ( f _C ) detected as a function of the filter cutoff frequency f _C with a reference propagation time t _ref for charge pulses conducted in a conductive manner through the entire operating means 20.

The comparison device 105 may comprise an arithmetic unit providing a comparison result of the detected signal propagation time t with the reference propagation time t _ref .

The reference propagation time t _ref for charge pulses conducted through the entire equipment 20 can be recorded, for example, during production or before commissioning of the equipment 20 with the aid of a charge calibrator 106 (see below). An artificially generated charge pulse is conducted through the entire equipment 20. The reference propagation time t _ref determined in this way corresponds to a total length L of the conducted signal propagation path between the connections of the equipment 20. A partial discharge in the equipment 20 occurs between these connections. The conducted signal propagation time t (f _C ) recorded as a function of the filter cutoff frequency f _C is always a fraction of the reference propagation time t _ref and corresponds to an equal fraction of the length L of the entire signal propagation path: $$\frac{x}{L}=\frac{t\left(\mathit{fc}\right)}{t_{\mathit{ref}}}$$

By comparing 305 the two signal propagation times, partial discharges in a winding of the equipment 20 can be localized at a length position x between the terminals of the equipment 20 without having direct access to the relevant winding of the equipment 20, since the underlying Measurements can be made at the connections of the equipment 20. With additional knowledge of the complex winding geometry of the equipment 20, an exact spatial localization of the point of origin of the PD can also be carried out.

The device 10 may further comprise a charge calibrator 106 for conducting 306 a charge pulse through the entire equipment 20.

Prior to the actual TE measurement, and therefore in Fig. 1 indicated as optional by a line pattern, an artificially generated TE pulse can be sent through the entire winding using a charge calibrator 106. For this purpose, the charge calibrator 106 is to be connected in an electrically conductive manner to the remote "N(eutral)" connection of the device 20. The charge pulse released there by the charge calibrator 106 propagates from the remote "N(eutral)" connection through the entire winding provided between the connections of the device 20 to the "P(phase)" connection close to the signal detection device 101 and, after a running time t _ref , leads to a change in the 301 electrical signal quantity detected there. The running time t _ref of this pulse serves as a reference for the running time that a pulse requires to run through the entire winding (total running time). The transit time t of a real PD pulse is specified relative to this reference in order to indicate the relative position of the origin of the PD within the winding. Of course, the charge calibrator 106 can alternatively be connected to the "P(h)ase" connection, while the signal acquisition then takes place via the "N(eutral)" connection.

Fig. 4 illustrates a method 30 for locating partial discharges in medium or high voltage equipment 20 according to an embodiment.

The method 30 can be carried out with the device 10 according to various embodiments.

Consequently, the above-mentioned device features and their advantages can be used analogously in the method.

For this purpose, the signal detection device 101 of the device 10 is as in Fig. 1 shown to be electrically connected to the near and far terminals of the equipment 20.

In step 301, the method 30 comprises detecting an electrical signal quantity of the operating means 20 by means of the signal detection device 101 of the apparatus 10.

In step 302, the method 30 comprises low-pass filtering of the detected electrical signal quantity by means of a filter device 102 of the apparatus 10 as a function of a filter cutoff frequency f _C of the filter device 102.

The filter cutoff frequency f _C may be no more than 1 MHz, preferably no more than 100 kHz, and more preferably no more than 50 kHz.

In step 303, the method 30 may further comprise gradually reducing the filter cutoff frequency fc starting from an initial filter cutoff frequency f _C,0 until a signal propagation time t detected at the reduced filter cutoff frequency f _C exceeds a predetermined absolute signal propagation time threshold t _th or exceeds a signal propagation time duration t ₀ detected at the initial filter cutoff frequency f _C,0 by a predetermined relative signal propagation time ratio N. $$t\left(f_C\right)>t_{\mathit{th}}\mathrm{oder}t\left(f_C\right)>N\cdot t\left(f_{C,0}\right)$$

A step size when reducing 303 the filter cutoff frequency f _C can be at least 0.1 kHz, preferably 1 kHz and even more preferably 10 kHz.

This limits the duration of a TE examination of a test object.

The predetermined relative signal propagation time ratio N can be at least 2, preferably 5 and particularly preferably 10.

This additionally or alternatively enables a relative setting of a threshold value for detecting a sudden increase in the signal propagation time t when gradually reducing 303 the filter cutoff frequency f _C .

In step 304, the method 30 comprises detecting a signal propagation time t of the low-pass filtered electrical signal quantity by means of a time detection device 104 of the device 10.

In step 305, the method 30 comprises comparing the signal propagation time t detected as a function of the filter cutoff frequency f _C with a reference propagation time t _ref for charge pulses conducted through the entire equipment 20 by means of a comparison device 105.

The method 30 may further comprise, in step 306, conducting a charge pulse through the entire operating means 20 by means of a charge calibrator 106 of the device 10, wherein the step 306 in Fig. 4 and the charge calibrator 106 in Fig. 1 are indicated as optional by line patterns. The charge calibrator 106 is to be electrically connected to the remote terminal of the equipment 20 in order to introduce an artificially generated TE pulse there and, based thereon, to record a reference propagation time t _ref for charge pulses conducted through the entire equipment 20.

Claims (13)

1. An apparatus (10) for locating a partial discharge in a medium- or high-voltage operating means (20), comprising

   a signal detection device (101) for detecting (301) an electrical signal variable of the operating means (20);

   a filter device (102) for low-pass filtering (302) of the detected electrical signal variable depending on a filter cut-off frequency (fc);

   a time detection device (104) for detecting (304) a signal propagation time (t) of the low-pass-filtered electrical signal variable; and

   a comparison device (105) for comparing (305) the detected signal propagation time (t) detected depending on the filter cut-off frequency (fc) with a reference propagation time (t_ref) for a charge pulse conducted through the operating means (20) in order to determine a location of the partial discharge in the operating means depending on the result of the comparison,

   characterized in

   that the filter device (102) is set up for stepwise reducing (303) the filter cut-off frequency (fc) starting from an initial filter cut-off frequency (f_C,0) until a signal propagation time (t) detected at the reduced filter cut-off frequency (fc) exceeds a predefined absolute signal propagation time threshold value (t_th) or exceeds a signal propagation time period (t₀) detected at the initial filter cut-off frequency (f_C,0) by a predefined relative signal propagation time ratio (N).
2. The apparatus (10) of claim 1, wherein a step size when reducing the filter cut-off frequency (fc) is at least 10 kHz.
3. The apparatus (10) of claim 1 or claim 2, wherein the predefined relative signal propagation time ratio (N) is at least 10.
4. The apparatus (10) of any one of the preceding claims, wherein the filter cut-off frequency (fc) is at most 1 MHz, preferably at most 100 kHz, and more preferably at most 50 kHz.
5. The apparatus (10) of any one of the preceding claims, further comprising a charge calibrator (106) for wired conduction (306) of a charge pulse through the operating means (20) for determining the reference propagation time (t_ref).
6. The apparatus (10) of any one of the preceding claims, wherein the detected electrical signal variable comprises digital voltage values, and wherein the signal detection device (101) comprises a voltmeter that provides digital voltage values.
7. The apparatus (10) of any one of the preceding claims, wherein the filter device (102) comprises a digital low-pass filter.
8. The apparatus (10) of any one of the preceding claims, wherein the time detection device (103) comprises a timer that provides digital time values.
9. The apparatus (10) of any one of the preceding claims, wherein the comparison device (105) comprises an arithmetic unit that provides a comparison result of the detected signal propagation time (t) with the reference propagation time (tref).
10. A method (30) for locating a partial discharge in a medium- or high-voltage operating means (20), comprising

    detecting (301) an electrical signal variable of the operating means (20); low-pass filtering (302) of the detected electrical signal variable depending on a filter cut-off frequency (fc);

    detecting (304) a signal propagation time (t) of the low-pass-filtered electrical signal variable; and

    comparing (305) the detected signal propagation time (t) detected depending on the filter cut-off frequency (fc) with a reference propagation time (t_ref) for a charge pulse conducted through the operating means (20) in order to determine a location of the partial discharge in the operating means depending on the result of the comparison,

    characterized by

    stepwise reducing (303) the filter cut-off frequency (fc) starting from an initial filter cut-off frequency (f_C,0) until a signal propagation time (t) detected at the reduced filter cut-off frequency (fc) exceeds a predefined absolute signal propagation time threshold value (t_th) or exceeds a signal propagation period (t₀) detected at the initial filter cut-off frequency (f_C,0) by a predefined relative signal propagation time ratio (N).
11. The method (30) of claim 10, further comprising:
    wired conducting (306) of a charge pulse through the operating means (20) for determining the reference propagation time (t_ref) based on a running time of the charge pulse through the operating means before locating the partial discharge.
12. The method (30) of claim 10 or claim 11, further comprising:

    determining a frequency range of the electrical signal variable in which a low-frequency component of the partial discharge dominates over a highfrequency component of the partial discharge; and

    detecting (304) the signal propagation time (t) of the electrical signal variable in the determined frequency range.
13. The method (30) of any one of claims 10-12, wherein the method (30) is carried out using the apparatus (10) of any one of claims 1-9.

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